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MillimeterGreen Zone Step by Step
Mar 26, 2010 12:00 PM, By Ellen Wolff
When Director Paul Greengrass took on Universal Pictures' Green Zone, a major challenge was capturing the look of wartime Iraq without being able to film there. Iconic landmarks such as Baghdad's Hands of Victory arches, with their giant crossed swords, needed to be included, so CG versions had to be merged convincingly with live action. To meet this challenge, Greengrass tapped the visual effects crew at London's Double Negative (DNeg), which he'd collaborated with on The Bourne Ultimatum.
An archetypal example of DNeg's work was a sequence in which Green Zone star Matt Damon drives a Humvee past the crossed swords, as well as a variety of military hardware, rubble, and extras. "We started the shot panning from some journalists having their photo taken and panned with the Humvee as it drives past an armored vehicle in the foreground," says DNeg Visual Effects Supervisor Charlie Noble. "We ended up looking down the line with the crossed swords. But when we photographed this in Morocco, all we had was the Humvee and the journalists and a large expanse of tarmac. That was it."
But the DNeg crew wasn't going to wait until postproduction to tackle the CG architecture and military hardware models that they'd need to add to the shot. They used online visual references (such as Google Earth) to build rough-shaded models in Autodesk Maya and brought the models on location so that Greengrass could compose the shot with the CG in mind. "We took along a virtual overlay system," Noble says. "We had an HD camera positioned at a good vantage point on set, and we brought in the relevant CG models which had been built to a good previz level. After the camera was set up, we'd snap our CG models to the location so that Paul could pan our high-res camera around the set and see on a monitor what we'd be adding to the scene. That was a really useful lineup reference for the camera crew.
"We also had a crane on set, which we set so that it lined up with where our CG arches would be," Noble says. The crane, which would later be rotoscoped out, provided a placeholder to ensure that the space required for the CG arches wouldn't be cut off.
This overlay system was particularly crucial in a shot where the live-action photography needed to be placed in the mid-ground with foreground and background CG elements around it. "We planned to later put in a huge CG [Bradley armored vehicle] in the extreme foreground," Noble says. "The [vehicle] needed to have a driver with his head poking out of the turret. So when we shot the plate we brought in an appropriately sized blue box for the guy to stand on so he'd be at the correct height. It looked a little funny during shooting, but it's good to get as much in the plate as you can."
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